It is desirable to be able to have recourse to an industrial component, such as, in particular, a mechanical component, before launching the full-scale manufacture thereof. Currently, in order to construct models of such components, it is necessary firstly to create dimensioned drawings, in the drawing office, based on numerical information defining the shape of the component. For some years, the method of "Computer-Aided Design" (CAD) has been used to define the shape of this component.
It is known to provide a production method and a production device with models of industrial components by direct use of the numerical data available in the output memories of the computer in order to construct the models of components without being obliged to pass via drawings, or to have to employ numerical-control machining machines, such as mills, lathes, etc.
Methods and devices proposed for the construction of models using CAD rely on laser-induced chemical polymerization. The servo-controlled movement of one or more laser beams, possibly focused at the same spot, permits local polymerization of an advantageously polyfunctional monomer and, progressively, the construction of the component.
For example, the document [1] describes a method whose general principle for constructing a component relies on the use of an apparatus comprising a tank which contains the liquid photopolymerizable monomer (or oligomer or mixture of the two) and flush with the level of this liquid is a movable platform which descends, step by step, during the operation. At the surface of the liquid, the laser beam traces successive cross-sections of the object to be produced, by virtue of a set of electronic deflection mirrors, driven by the database of the CAD system. The software has subdivided the virtual model of the article beforehand into a multitude of thin slices. Progressively as each slice solidifies, the "sculptured" model sinks slowly into the tank: with a 10-mW laser, this system permits a component 30 mm in height to be created in 50 minutes, with an accuracy of the order of one tenth of a millimeter. The model can be created from all kinds of (plastic) materials, in a great variety of colours, with different hardnesses and a wide range of abrasion resistances [3, 4].
This type of method, which requires a material being, in the initial state, in a liquid or pasty form, has a drawback when it is desired to manufacture components which include hanging parts. Once the orientation of the component has been fixed with respect to the vertical (defined by gravity during the manufacturing phase), it may occur that certain portions are not supported either by another part of the component or by the bed on which the component rests (cf. FIGS. 1A-1D).
In this case, when the light radiation comes to solidify the first part of this portion, the volume just solidified is not attached to any other solid and is isolated in the liquid. In general, the densities of the liquid and solid are different and the volume runs the risk of "flowing" if the surface tension is not sufficient to hold it at the surface. In addition, when putting the next layer of liquid in place, the component is moved, during construction, with respect to the liquid level. Since this movement is performed by means of the mechanical arm supporting it, it is impossible to impart the movement to the isolated volume, which will therefore no longer be integral with the rest of the component throughout the rest of the manufacture.
In order to solve this problem, current users of this type of method add to the component, prior to its manufacture, "supports" permitting the hanging portions to be rendered integral with the component or with the bed supporting it (cf. FIGS. 2A-2D).
Specifically, this addition is performed by modification of the database stemming from the CAD system which was used in the design of the component. It should be pointed out that this step is not a simple operation and it has many drawbacks, for the following reasons:
mastery of the CAD system which was used in the design of the component is necessary on the part of the user of a machine for manufacturing an article in 3 dimensions, which problem is aggravated by the fact that very many different CAD systems exist and that these are not completely compatible; PA1 removal of the supports, once manufacture has been completed, is an operation which, if precautions are not taken, or if the supports are poorly placed, can damage the component; PA1 it is quite difficult to automate this step, since the placing of the supports, so as to make it easier to remove them (while at the same time ensuring correct manufacture of all the hanging portions), requires a great deal of experience, difficult to formalize; PA1 finally, certain components may have hanging portions which are very difficult to access, making them virtually impossible to manufacture by this type of method (cf. FIG. 3). PA1 the addition of wet powder to a component is extremely simple to automate: all that is necessary is that the component be entirely encompassed (to a sufficient thickness); PA1 it is completely pointless to add supports, this resulting in a spectacular decrease in the "computing cost" of the manufacture of a component (some users of the method consider that the manufacturing time for a slightly complex component is 80% composed of computing work); PA1 the final cleaning runs less of a risk of damaging the component than when it is necessary to detach the supports therefrom; PA1 some components, impossible to manufacture by that method (for example when it is impossible to add supports since they could not be removed from the component on completing its manufacture) become feasible, still without imposing a computing cost. PA1 the portions located at the periphery of the powdery medium may be considered as isolated from the rest of the component and they run the risk of not being integral with it during a movement; PA1 it is necessary that the liquid should not remain contaminated by particles of powder once the manufacture of the component is completed.
Other rapid prototyping methods, such as, for example, the one described in the document [2], solve this problem by using a solid material, which ensures that no isolated portion can "flow" or move during the manufacture. However, these methods have other drawbacks compared to the methods using liquid, in particular as regards the loss of useful material during manufacture.